Drop/insert channel selecting system

Abstract

A drop/insert selecting system for an optical transmission system has a decreased circuit scale, by providing a switching unit (4,4') having a plurality of input terminals for receiving a plurality of input channels and a plurality of output terminals, each of the input channels conveying a frame synchronization signal and a channel number. At at least one drop/insert unit (51,52,51',52') is provided for sequentially generating channel preselection signals until a frame synchronization is established and for dropping or inserting necessary signals from or into a corresponding one of the necessary channels incorporated into the drop/insert units when a frame synchronization is established. A channel selecting unit (6,6a,6b) is provided for generating a plurality of channel selecting signals in response to each of the channel preselection signals, each of the channel selecting signals functioning to connect each of the output terminals to one of the plurality of input terminals. The remaining output terminals of the switching unit are connected to through-channels to which no drop/insert units are connected.

We claim: 
     
       1. A drop/insert selecting system for dropping or inserting signals from or into a plurality of channels passing between input channels and output channels, comprising: drop/insert means, coupled to the output channels, for sequentially generating channel preselecting signals until a frame synchronization state is established and for dropping or inserting signals from or into a corresponding one of the output channels when the frame synchronization state is established;   channel selecting means for generating first and second groups of channel selecting signals in response to the channel preselecting signals; and   switching means, having a plurality of input terminals coupled to the input channels and having first and second groups of output terminals, the first group of the output terminals operatively connected to said drop/insert means and the second group of the output terminals operatively connected to the corresponding output channels as through-channels without any connection to said drop/insert means, for selectively connecting each of the output terminals of the first group to one of the input terminals in response to the first group of the selecting signals and for selectively connecting each of the output terminals of the second group to one of the input terminals in response to the second group of the selecting signals.   
     
     
       2. A drop/insert selecting system as claimed in claim 1, wherein the plurality of input terminals comprise first, second, third and fourth input terminals;   wherein the plurality of output terminals comprise first and second output terminals of the second group and third and fourth output terminals of the first group;   wherein said drop/insert means comprises first and second drop/insert units, operatively connected to said first and said second output terminals, respectively; and   wherein the through-channels comprise first and second through-channels, operatively connected to the third and the fourth output terminals, respectively.   
     
     
       3. A drop/insert selecting system as claimed in claim 2, wherein each of said drop/insert units comprises: frame synchronization detecting means, operatively connected to a corresponding one of the output terminals, for outputting an out of frame signal upon detecting an out of frame synchronization state in the channel output from the corresponding output terminal;   comparing means, operatively connected to a corresponding one of the output terminals, for outputting a non-coincidence signal upon detecting non-coincidence between the corresponding output terminal and a previously stored channel number indicating the channel to be used for one of dropping and inserting the necessary signals; and   preselecting signal generating means, operatively connected to said frame synchronization detecting means and said comparing means, for generating at least first and second bits of a first channel preselecting signal for selecting one of the input terminals to be connected to the output terminal connected to the drop/insert unit under consideration, the first and second bits being changed with a predetermined period until both the out of frame and the non-coincidence signals disappear.   
     
     
       4. A drop/insert selecting system as claimed in claim 3, further comprising: an out of frame protection circuit, operatively connected to said frame synchronization detecting means, for effecting front and rear protection of the out of frame signal from said frame synchronization detecting means;   a non-coincidence signal protection circuit, operatively connected to said comparing means, for effecting front and rear protection of the non-coincidence signal from said comparing means; and   a reframe protection circuit, operatively connected between the outputs of said out of frame protection circuit and said switching means, and between the output of said non-coincidence protection circuit and said switching means, for effecting a rear protection of the signal output from said out of frame protection circuit or said non-coincidence protection circuit.   
     
     
       5. A drop/insert selecting system as claimed in claim 3, wherein said preselecting signal generating means comprises: clock signal generating means for generating a clock signal; and   frequency dividing means, operatively connected to said clock signal generating means, to said frame synchronization detecting means, and to said comparing means, for generating the first and second bits in response to the clock signal until both of the out of frame signal and the non-coincidence signal disappear.   
     
     
       6. A drop/insert selecting system as claimed in claim 5, further comprising: counter means, operatively connected to said frequency dividing means, for counting at least a maximum average reframing time from detection of an out of frame state.   
     
     
       7. A drop/insert selecting system as claimed in claim 2, wherein said channel selecting means comprises: first and second pairs of lines, operatively connected to said first and said second drop/insert units, respectively, the first pair of lines for directly passing first and second bits of a first channel preselecting signal of the second group, output from said first drop/insert unit, to said switching means, as a first channel selecting signal of the first group and directly passing first and second bits of a second channel preselecting signal output from said second drop/insert unit, to said switching means, as a second channel selecting signal of the first group for selecting one of the input terminals to be connected to the first output terminal and another one of the input terminals to be connected to the second output terminal, respectively;   a first NOT gate for inverting the first bit of the first channel preselecting signal output a first bit of a third channel selecting signal of the second group for selecting one of the input terminals to be connected to the third output terminal;   a second NOT gate for inverting the second bit of the first channel preselecting signal to output a second bit of a fourth channel selecting signal of the second group for selecting one of the input terminals to be connected to the fourth output terminal;   a third NOT gate for inverting the first bit of the second channel preselecting signal to output a first bit of the fourth channel selecting signal; and   a fourth NOT gate for inverting the second bit of the second channel preselecting signal to output a second bit of the third channel selecting signal.   
     
     
       8. A drop/insert selecting system as claimed in claim 7, wherein each of said drop/insert units comprises: frame synchronization detecting means, operatively connected to a corresponding one of the output terminals, for outputting an out of frame signal upon detecting an out of frame synchronization state in the channel output from the corresponding output terminal;   comparing means, operatively connected to a corresponding one of the output terminals, for outputting a non-coincidence signal upon detecting non-coincidence between the channel number in the channel output from the corresponding output terminal and a previously stored channel number indicating the channel to be used for at least one of dropping and inserting the necessary signals; and   preselecting signal generating means, operatively connected to said frame synchronization detecting means and said comparing means, for generating the bits of the first and second channel preselecting signals for selecting one of the input terminals to be connected to the output terminal connected to the drop/insert unit under consideration, the bits of the first and second preselecting signals being changed with a predetermined period until both the out of frame and the non-coincidence signals disappear.   
     
     
       9. A drop/insert selecting system as claimed in claim 8, further comprising: an out of frame protection circuit, operatively connected to said frame synchronization detecting means, for effecting front and rear protection on the out of frame signal from said frame synchronization detecting means;   a non-coincidence signal protection circuit, operatively connected to said comparing means, for effecting front and rear protection of the non-coincidence signal from said comparing means; and   a reframe protection circuit, operatively connected between the outputs of said out of frame protection circuit and said switching means, and between the output of said non-coincidence signal protection circuit and said switching means, for effecting front protection and rear protection of the signal output from said out of frame protection circuit or said non-coincidence signal protection circuit.   
     
     
       10. A drop/insert electing system as claimed in claim 8, wherein said preselecting signal generating means comprises: clock signal generating means for generating a clock signal; and   frequency dividing means, operatively connected to said clock signal generating means, to said frame synchronization detecting means, and to said comparing means, for generating the channel preselecting signals in response to the clock signal, the out of frame signal and the non-coincidence signal.   
     
     
       11. A drop/insert selecting system as claimed in claim 10, further comprising: counter means, operatively connected to said frequency dividing means, for counting at least a maximum average reframing time from the detection of an out of frame state.   
     
     
       12. A drop/insert selecting system as claimed in claim 2, wherein said switching means comprises a first, second, third, and fourth switching parts arranged to correspond to said first drop/insert unit, said second drop/insert unit, said first through-channel, and said second through-channel, respectively;   wherein each of said switching parts having the plurality of input terminals and one of the output terminals connected to a corresponding one of said first drop/insert unit, said second drop/insert unit, said first through-channel, and said second through-channel;   wherein said third switching part and said fourth switching part having means to fix, when said first or said second drop/insert unit is in an out of frame synchronization state, their switching positions determining the through channels.   
     
     
       13. A drop/insert selecting system for dropping or inserting signals from or into a plurality of channels passing between input channels and output channels, at least one of which is selectively used as a through-channel or a drop/insert channel based on the presence of a number of drop/insert units plugged into the system, comprising: drop/insert means, having at least a first drop/insert unit, each drop/insert unit of said drop insert means coupled to corresponding output channels, for sequentially generating channel preselecting signals until a frame synchronization state is established and for dropping or inserting signals from or into a corresponding one of the output channels when the frame synchronization state is established;   detecting means for generating a detecting signal indicating if said drop/insert means has presence of at least a second drop/insert unit coupled to corresponding output channels;   channel selecting means for generating a first set of at least one channel selecting signal in response to the channel preselecting signals and for generating a second set of at least one channel selecting signal in response to both the channel preselecting signals and the detecting signal;   switching means, having a plurality of input terminals coupled to the input channels and having a plurality of output terminals, at least one of the output terminals operatively connected to said drop/insert means and any remaining output terminals operatively connected to corresponding output channels as through-channels without any connection to said drop/insert means depending on the number of drop/insert units plugged into the system, for selectively connecting each of the output terminals to each of the input terminals in response to the selecting signals.   
     
     
       14. A drop/insert selecting system as claimed in claim 13, wherein said switching means comprises first, second, third and fourth input terminals and first, second, third and fourth output terminals;   wherein said drop/insert means comprises and second drop insert units, and third and fourth optional drop/insert units, operatively connected to the first, the second, the third, and the fourth output terminals, respectively, the third and the fourth optional drop/insert units being optionally plugged into said drop/insert selecting system; and   wherein said detecting means comprises means for generating the detecting signal indicating that said third and said fourth drop/insert units are plugged into said drop/insert system.   
     
     
       15. A drop/insert selecting system as claimed in claim 14, wherein said channel selecting means comprises: a first and second pair of lines, operatively connected to said first and said second drop/insert units, respectively, the first pair for directly passing first and second bits of a first channel preselecting signal, output from said first drop/insert unit, to said switching means, as a first channel selecting signal of the first set of channel selecting signals and directly passing first and second bits of a second channel preselecting signal output from said second drop/insert unit, to said switching means, as a second channel selecting signal of the first set of channel selecting signals for selecting one of the input terminals to be connected to the first output terminal and another input terminal to be connected to the second output terminal, respectively;   a first NOT gate for inverting the first bit of the first channel preselecting signal;   a second NOT gate for inverting the second bit of the first channel preselecting signal;   a third NOT gate for inverting the first bit of the second channel preselecting signal;   a fourth NOT gate for inverting the second bit of the second channel preselecting signal;   a first gate circuit having a first input connected to the output of said first NOT gate and a second input connected to a first bit of a third channel preselecting signal, for outputting, as a first bit of a third channel selecting signal of the second set of channel selecting signals, either the first bit of the third channel preselecting signal or the output of said first NOT gate, depending on whether the detecting signal indicates said third drop/insert unit si plugged into said drop/insert selecting system respectively;   a second gate circuit having a first input connected to the output of said fourth NOT gate and a second input connected to a second bit of the third channel preselecting signal, for outputting, as a second bit of the third channel selecting signal of the second set of channel selecting signals, either the second bit of the third channel preselecting signal or the output of said fourth NOT gate, depending on whether the detecting signal indicates said third drop/insert unit is plugged into said drop/insert selecting system respectively;   a third gate circuit having a first input connected to the output of said third NOT gate and a second input connected to a first bit of a fourth channel preselecting signal, for outputting, as a first bit of a fourth channel selecting signal of the second set of channel selecting signals, either the first bit of the fourth channel preselecting signal or the output of said third NOT gate, depending on whether the detecting signal indicates said fourth drop/insert unit is plugged into said drop/insert selecting system respectively; and   a fourth gate circuit having a first input connected to the output of said second NOT gate and a second input connected to a second bit of the fourth channel preselecting signal, for outputting, as a second bit of the fourth channel selection signal of the second set of channel selecting signals, either the second bit of the fourth channel preselecting signal or the output of said second NOT gate, depending on whether the detecting signal indicates said fourth drop/insert until is plugged into said drop/insert selecting system respectively;   wherein the outputs of said first and said second gate circuits being the third channel selecting signal for selecting one of the input terminals of said switching means to be connected to the third output terminal of said switching means;   wherein the outputs of said third an said fourth gate circuits being the fourth channel selecting signal for selecting one of the input terminals of said switching means to be connected to the fourth output terminal of said switching means.   
     
     
       16. A drop/insert selecting system as claimed in claim 15, wherein each of said drop/insert units comprises: frame synchronization detecting means, operatively connected to a corresponding one of the output terminals, for outputting an out of frame signal upon detecting an out of frame synchronization state in the channel output from the corresponding output terminal;   comparing means, operatively connected to a corresponding one of the output terminals, for outputting a non-coincidence signal upon detecting non-coincidence between the channel number in the channel output from the corresponding output terminal and a previously stored channel number indicating the channel to be used for one of dropping and inserting the necessary signals; and   preselecting signal generating means, operatively connected to said frame synchronization detecting means and said comparing means, for generating the bits of the channel preselecting signals for selecting one of the input terminals to be connected to the output terminal connected to the drop/insert unit under consideration, the bits of the channel preselecting signals being changed with a predetermined period until both the out of frame and the non-coincidence signals disappear.   
     
     
       17. A drop/insert selecting system as claimed in claim 16, further comprising: an out of frame protection circuit, operatively connected to said frame synchronization detecting mans, for effecting front and rear protection of the out of frame signal from said frame synchronization detecting means;   a non-coincidence signal protection circuit, operatively connected to said comparing means, for effecting front and rear protection of the non-coincidence signal from said comparing means; and   a reframe protection circuit, operatively connected between the outputs of said out of frame protection circuit and said switching means, and between the output of said non-coincidence signal protection circuit and said switching means, for effecting a front protection and a rear protection of the signal output from said out of frame protection circuit or said non-coincidence signal protection circuit.   
     
     
       18. A drop/insert selecting system as claimed in claim 16, wherein said preselecting signal generating means comprises: clock signal generating means for generating a clock signal; and   frequency dividing means, operatively connected to said clock signal generating means, to said frame synchronization detecting means, and to said comparing means, for generating the preselecting signals in response to said clock signal until both of the out of frame signal and the non-coincidence signal disappear.   
     
     
       19. A drop/inset selecting system as claimed in claim 18, further comprising: counter means, operatively connected to said frequency dividing means, for counting at least the maximum average reframing time from the detection of an out of frame state.   
     
     
       20. A drop/insert selecting system for dropping or inserting signals from or into a plurality of channels passing between input channels and output channels, at least one of which is selectively used as a through-channel or a drop/insert channel based on the presence of a number of drop/insert units plugged into the system, comprising: drop/insert means, having at least a first drop/insert unit, each drop/insert unit of said drop/insert means coupled to corresponding output channels, for sequentially generating channel preselecting signals until a frame synchronization state is established and for dropping or inserting signals from or into a corresponding one of the output channels when the frame synchronization state is established;   detecting means for generating a detecting signal indicating if said drop/insert means has presence of at least a second drop/inset unit coupled to corresponding output channels;   channel selecting means for generating a plurality of channel selecting signals in response to both the channel preselecting signals and the detecting signal; and   switching means, having a plurality of input terminals coupled to the input channels and having a plurality of output terminals, at least one of the output terminals operatively connected to said drop/insert means and any remaining output terminals operatively connected to corresponding output channels as through-channels without any connection to said drop/.insert means depending on the number of drop/insert units plugged into the system, for selectively connecting each of the output terminals to each of the input terminals in response to the selecting signals.   
     
     
       21. A drop/insert selecting system as claimed in claim 20, wherein said switching means comprises first, second, third an fourth input terminals and first, second, third an fourth output terminals;   wherein said drop/insert means comprises first, second, third and fourth optional drop/insert units, optionally plugged into said drop/insert selecting system, and operatively connected to the first, second, third and fourth output terminals, respectively, when plugged into said drop/insert selecting system; and   wherein said detecting means comprises means for generating the detecting signal indicating whether said first, second, third and fourth drop/insert units are plugged into said drop/insert selecting system.   
     
     
       22. A drop/insert selecting system as claimed in claim 21, wherein each of said drop/insert units comprises: frame synchronization detecting means, operatively connected to a corresponding one of the output terminals for outputting an out of frame signal upon detecting an out of frame synchronization state in the channel output from the corresponding output terminal;   comparing means, operatively connected to a corresponding one of the output terminals, for outputting a non-coincidence signal upon detecting non-coincidence between the channel number in the channel output from the corresponding output terminal and a previously stored channel number indicating the channel to be used for one of dropping and inserting the necessary signals; and   preselecting signal generating means, operatively connected to said frame synchronization detecting means and said comparing means, for generating preselecting signals for selecting one of the input terminals to be connected to the output terminal connected to the drop/insert unit under consideration, the preselecting signals being changed with a predetermined period until both the out of frame and the non-coincidence signals disappear.   
     
     
       23. A drop/insert selecting system as claimed in claim 22, further comprising: an out of frame protection circuit, operatively connected to said frame synchronization detecting means, for effecting front and rear protection on the out of frame signal from said frame synchronization detecting means;   a non-coincidence signal protection circuit, operatively connected to said comparing means, for effecting front and rear protection of the non-coincidence signal from said comparing means; and   a reframe protection circuit, operatively connected between the outputs of said out of frame protection circuit and said switching means, and between the output of said non-coincidence signal protection circuit and said switching means, for effecting a front protection and a rear protection of the signal output from said out of frame protection circuit or said non-coincidence signal protection circuit.   
     
     
       24. A drop/insert selecting system as claimed in claim 22, wherein said preselecting signal generating means comprises: clock signal generating means for generating a clock signal; and   frequency dividing means, operatively connected to said clock signal generating means, to said frame synchronization detecting means, and to said comparing means, for generating the channel preselecting signals in response to the clock signal until both the out of frame signal and the non-coincidence signals disappear.   
     
     
       25. A drop/insert selecting system as claimed in claim 24, further comprising: counter means, operatively connected to said frequency dividing means, for counting at least a maximum average reframing time from the detection of an out of frame state.   
     
     
       26. A drop/insert selecting system as claimed in claim 21, wherein said channel selecting means comprises: a first NOT gate for inverting a first bit of a first channel preselecting signal;   a second NOT gate for inverting a second bit of the first channel preselecting signal;   a third NOT gate for inverting a first bit of a second channel preselecting signal;   a fourth NOT gate for inverting a second bit of the second channel preselecting signal;   a fifth NOT gate for inverting a first bit of a third channel preselecting signal;   a sixth NOT gate for inverting a second bit of the third channel preselecting signal;   a seventh NOT gate for inverting a first bit of a fourth channel preselecting signal;   an eighth NOT gate for inverting a second bit of the fourth channel preselecting signal;   a first gate circuit having a first input connected to the output of said first NOT gate and a second input connected to a first bit of the third channel preselecting signal, for outputting, as a first bit of a third channel selecting signal, either the first bit of the third channel preselecting signal or the output of said first NOT gate, depending on whether the detection signal indicates said third drop/insert unit is plugged into said drop/insert selecting system respectively;   a second gate circuit having a first input connected to the output of said fourth NOT gate and a second input connected to a second bit of the third channel selecting signal, for outputting, as a second bit of the third channel selecting signal, either the second bit of the third channel preselecting signal or the output of said fourth NOT gate, depending on whether the detecting signal indicates said third drop/insert unit is plugged into said drop/insert selecting system respectively;   a third gate circuit having a first input connected to the output of said third NOT gate and a second input connected to a first bit of the fourth channel preselecting signal, for outputting, as a first bit of a fourth channel selecting signal, either the first bit of the fourth channel preselecting signal or the output of said third NOT gate, depending on whether the detecting signal indicates said fourth drop/insert unit is plugged into said drop/insert selecting system respectively;   a fourth gate circuit having a first input connected to the output of said second NOT gate and a second input connected to a second bit of the fourth channel preselecting signal, for outputting, as a second bit of the fourth channel selecting signal, either the second bit of the fourth channel preselecting signal or the output of said second NOT gate, depending on whether the detecting signal indicates said fourth drop/insert unit is plugged into said drop/insert system selecting respectively;   a fifth gate circuit having a first input connected to the output of said fifth NOT gate and a second input connected to a first bit of the first channel preselecting signal, for outputting, as a first bit of a first channel selecting signal, either the first bit of the first channel preselecting signal or the output of said fifth NOT gate, depending on whether the detecting signal indicates said first drop/insert unit is plugged into said drop/insert selecting system respectively;   a sixth gate circuit having a first input connected to the output of said eighth NOT gate and a second input connected to a second bit of the first channel preselecting signal, for outputting, as a second bit of a first channel selecting signal, either the second bit of the first channel preselecting signal or the output of said eighth NOT gate, depending on whether the detecting signal indicates said first drop/insert unit is plugged into said drop/insert selecting system respectively;   a seventh gate circuit having a first input connected to the input of said seventh NOT gate and a second input connected to a first bit of the second channel preselecting signal, for outputting, as a first bit of a second channel selecting signal, either the first bit of the second channel preselecting signal or the output of said seventh NOT gate, depending on whether the detecting signal indicates said third drop/insert unit is plugged into said drop/insert system selecting respectively;   an eighth gate circuit having a first input connected to the output of said sixth NOT gate and a second input connected to a second bit of the second channel preselecting signal, for outputting, as a second bit of the second channel selecting signal, either the second bit of the second channel preselecting signal or the output of said sixth NOT gate, depending on whether the detecting signal indicates said fourth drop/insert unit is plugged into said drop/insert system selecting respectively;   wherein the outputs of said fifth and said sixth gate circuits being the first channel selecting signal for selecting one of the input terminals of said switching means to be connected to the first output terminal of said switching means;   wherein the outputs of said seventh and said eighth gate circuits being the second channel selecting signal for selecting one of the input terminals of said switching means to be connected to the second output terminal of said switching means;   wherein the outputs of said first and second gate circuits being the third channel selecting signal for selecting one of the input terminals of said switching means to be connected to the third output terminal of said switching means; and   wherein the outputs of said third and said fourth gate circuits being the fourth channel selecting signal for selecting one of the input terminals of said switching means to be connected to the fourth output terminal of said switching means.   
     
     
       27. A drop/insert selecting system as claimed in claim 21, wherein said third optional drop/insert unit and said fourth optional drop/insert unit are unplugged and their corresponding output channels are first and second through-channels;   wherein said switching means comprises a first, second, third, and fourth switching parts arranged to correspond to said first drop/insert unit, said second drop/insert unit, said first through-channel, and said second through-channel, respectively;   wherein each of said switching parts having said plurality of input terminals and one of said output terminals connected to a corresponding one of said first drop/insert unit, said second drop/insert unit, said first through-channel, and said second through-channel; and   wherein said third switching part and said fourth switching part having means to fix, when said first or said second drop/insert unit is in an out of frame synchronization state, their switching positions determining the through channels.